System and method for maintaining performance of battery-operated toothbrushes

ABSTRACT

The system periodically measures the battery voltage of the toothbrush and the current in a stator portion of the motor for the appliance. The amplitude of movement of the toothbrush workpiece is determined from the measured stator current. A circuit/control program changes the duty cycle or pulse width of the drive signal from the motor if the battery voltage drops below a first threshold value and a circuit or control program changes the drive frequency of the appliance if the amplitude of the workpiece movement falls below a first threshold value. A circuit/control program terminates the operation of the toothbrush if the voltage drops below a second threshold value or if the amplitude drops below a second threshold value, both of which are less than the respective first thresholds.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of and claims priority to Under 35 USC §120 fromprior U.S. patent application Ser. No. 12/513,034, filed Nov. 2, 2007,which is a national application of PCT Application No.PCT/IB2007/054462, filed Nov. 2, 2007 and claimed the benefit of U.S.Patent Application 60/856,642, filed Nov. 3, 2006, the entiredisclosures of which are incorporated herein by reference.

TECHNICAL FIELD

The invention relates generally to electric toothbrushes, and moreparticularly to a system for maintaining battery performance in such atoothbrush.

BACKGROUND OF THE INVENTION

Many personal care appliances, such as for example electrictoothbrushes, are powered by replaceable batteries. One disadvantage ofreplaceable batteries is that battery voltage declines with dischargeand use, with the voltage decreasing until the batteries finally die.Performance of the appliance begins to degrade significantly, however,well before the batteries actually die. Hence, there is a period of timeduring which, while the batteries are still operating, performance isadversely affected, which is undesirable. While all appliances withreplaceable batteries have this functional disadvantage, evenrechargeable batteries may have this disadvantage if their voltagedeclines between charging events.

It is thus desirable to be able to maintain battery voltage and thusconsistent performance from replaceable and rechargeable batteries,above a specified threshold, in order to maintain a desired level ofperformance during the life of the appliance.

SUMMARY OF THE INVENTION

Accordingly one embodiment is a system for maintaining performance of anelectric toothbrush powered by a battery, comprising: a system formeasuring the battery voltage of the electric toothbrush and/or thecurrent value in a stator portion of the motor for the electrictoothbrush from which current value the corresponding amplitude ofmovement of the workpiece of the toothbrush is then obtained; acircuit/program routine for changing the duty cycle or pulse width forthe drive signal of the motor if the battery voltage drops below a firstvoltage threshold value and/or a circuit/program routine for changingthe drive signal frequency if the amplitude falls below a firstamplitude threshold value, to increase the amplitude of movement of theworkpiece; and a circuit/program routine for terminating the operationof the appliance if the battery voltage drops below a second voltagethreshold value which is lower than the first voltage threshold valueand/or if the workpiece amplitude drops below a second amplitudethreshold value which is lower than the first amplitude threshold value.

Another arrangement is a system for maintaining performance of anelectric toothbrush, powered by a battery, comprising: a system formeasuring the battery voltage of the electric toothbrush; acircuit/program routine for changing the duty cycle or pulse width ofthe drive signal for the motor for the electric toothbrush if thebattery voltage drops below a first threshold value; and acircuit/program routine for terminating the operation of the toothbrushif the voltage drops below a second threshold value which is lower thanthe first threshold value.

Still another arrangement is a system for maintaining performance of anelectric toothbrush, powered by a battery, comprising: a system formeasuring the current in a stator portion of a motor supplying a drivesignal for the electric toothbrush and for determining the amplitude ofmovement of a brushhead workpiece from the measured stator current; acircuit/program routine for changing the drive frequency of theappliance if the amplitude of movement of the workpiece falls below afirst threshold value, to increase the amplitude of the workpiece tomaintain performance of the appliance; and a circuit/program routine forterminating the operation of the appliance if the amplitude of movementof the workpiece drops below a second threshold value which is lowerthan the first threshold value.

A still further aspect of the invention is a method for maintainingperformance of an electric toothbrush powered by a battery, comprisingthe steps of: measuring the battery voltage of the electric toothbrushand/or the current in a stator portion of the motor for the electrictoothbrush from which the amplitude of movement of the toothbrush isthen obtained; changing the duty cycle or pulse width of the drivesignal for the motor if the battery voltage drops below a firstthreshold value and/or changing the drive signal frequency of theappliance if the amplitude falls below a first amplitude threshold valueto increase the amplitude of movement of the workpiece; and terminatingthe operation of the appliance if the battery voltage drops below asecond voltage threshold value and/or if the workpiece amplitude dropsbelow a second amplitude threshold.

A still further aspect of the invention is a method for maintainingperformance of an electric toothbrush powered by a battery, comprisingthe steps of: measuring the battery voltage of the electric toothbrush;changing the duty cycle or pulse width of the drive signal for the motorfor the electric toothbrush if the battery voltage drops below a firstthreshold value; and terminating the operation of the toothbrush if thevoltage drops below a second threshold value which is lower than thefirst threshold value.

Another aspect of the invention is a method for maintaining performanceof an electric toothbrush powered by a battery, comprising the steps of:measuring the current in a stator portion of a motor supplying the drivesignal for the electric toothbrush and for determining the amplitude ofmovement of the brushhead workpiece from the measured stator current;changing the drive signal frequency if the amplitude of movement of theworkpiece falls below a first threshold value, so as to increase theamplitude of the workpiece to maintain performance of the appliance; andterminating the operation of the appliance if the amplitude of movementof the workpiece falls below a second threshold value which is lowerthan the first threshold value.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the elements of a power toothbrushwhich incorporates the system described herein.

FIGS. 2A and 2B are diagrams showing the decline in voltage andperformance over time relative to the number of brushings for anuncompensated appliance and similar diagrams for an appliance using thecompensation system described herein.

FIG. 2C is a diagram similar to FIGS. 2A and 2B showing multipleadjustments relative to performance.

FIG. 3 is a diagram showing performance of an appliance over a portionof its lifetime for an uncompensated appliance and an appliance usingthe compensation system described herein.

BEST MODE FOR CARRYING OUT THE INVENTION

As discussed above, replaceable batteries in oral care appliances, suchas electric toothbrushes, discharge over time, with the battery voltagedecreasing with the discharge. In the present embodiment, at a selectedtime during operation of the appliance, the battery voltage and/or thecurrent through the stator portion of the motor driving the appliance isdetermined. From that information, a characteristic of the motor drivesignal, such as duty cycle, is adjusted to compensate for the decline inbattery voltage or, in the case of an appliance with a resonant drivesystem, the drive frequency can be adjusted to increase the efficiencyof the apparatus. These adjustments maintain performance of theappliance for a number of additional brushing events beyond which thedecline in battery voltage would have resulted in degradation ofperformance below a minimum acceptable level.

FIG. 1 shows a block diagram of an electric toothbrush. It includesreplaceable batteries 12 and an electronic control unit 14. Theelectronic control unit 14 produces a drive signal which is applied toappliance stator 16 (motor), which drives a brushhead assembly 18 whichfor illustration includes a magnet arrangement 19 and a spring 19A. Thebrushhead assembly 18 includes a brushhead workpiece 20. The brushheadassembly 18 vibrates in a selected pattern, producing workpiece actionfor cleaning of teeth. A detailed description of one such embodiment isset forth in U.S. Pat. No. 5,189,751 the contents of which are herebyincorporated by reference. It should be understood, however, that suchembodiment is illustrative of one electric power toothbrush; theinvention disclosed herein is not limited to such an embodiment.

In a first arrangement of the present embodiment, which includesreplaceable batteries, the drive system for the toothbrush is a resonantsystem, in which the frequency of the drive signal to the motor from theelectronic control unit 14 is close to, if not the same as, the naturalresonant frequency of the appliance. In this arrangement, control unit14, which includes a microprocessor and a stored control program,measures the voltage from battery 12 and/or the current through stator16 at a selected time during the lifetime of operation of the battery,after each brushing event or a specified number, e.g. 30, of brushingevents. The control unit includes a standard algorithm which relates thevalue of the stator current to a corresponding amplitude of movement ofbrushhead workpiece 20, with amplitude being an indication ofperformance of the appliance.

The control unit 14 thus can have both battery voltage and workpieceamplitude to analyze. One or both of the following processes is thenused to make adjustments which maintain the consistency of performanceof the appliance even though the charge of the battery (and the batteryvoltage) has decreased. The action of an uncompensated arrangement isillustrated in FIG. 2A, which shows battery voltage 22 declining over aspecific number of uses, with performance (amplitude) 24 also declining.The performance line 24 generally follows voltage line 22. In theembodiment shown, performance line 24 crosses a threshold value ofacceptable performance 26 after a certain number of uses. Acceptableperformance is generally defined as clinically effective results. FIG.2A thus shows that performance is below an acceptable level for a time(a certain number of brushings) even though the appliance continues tooperate before the battery voltage goes to zero, which prevents anyfurther operation.

In a first mode, for a resonant drive system, the amplitude of movementof the brushhead workpiece (determined from the stator current) iscompared with a first amplitude threshold. This is done, as indicatedabove, after each or a selected number of brushing events have occurred,for example in the range of 30-brushings, although this could vary,depending on the particular toothbrush and the battery. If the amplitudehas fallen below a first threshold at that point, the drive frequency isadjusted to increase the efficiency of the toothbrush and hence theamplitude.

In this arrangement, during manufacture of the appliance, an initialdrive frequency is established relative to the natural resonantfrequency of the appliance such that the toothbrush is operating at anefficiency of less than 100%, i.e. in the range of 60-70%, for example.This leaves room for increasing efficiency by changing the drivefrequency. Usually the difference between the two frequencies is in arange of up to 7 Hz.

When the amplitude of movement of the brushhead is below a firstamplitude threshold, the drive frequency is changed so that an increasein operating efficiency results. This requires a slight (a few Hz)increase or decrease in the drive frequency, depending on the particularappliance. The increase in efficiency results in an increase inamplitude for a given battery voltage, maintaining desired performanceof the toothbrush for an additional number of brushings, for example, inthe range of 10-20 brushings. This is illustrated in FIG. 2B, in which,while the battery voltage still decreases, following line 27, theperformance of the toothbrush shown by line 28 remains above thethreshold line 29 for an extended period of time because of the increasein efficiency of the toothbrush occurring at least once during the lifeof the battery by a change in the drive frequency. FIG. 2C shows agenerally flat performance curve 28A, in response to the typical voltagedecline 27A, when there are multiple adjustments. While the presentsystem maintains performance during decline in battery voltage, thesystem operates when factors in addition to battery voltage decline,such as component age, affect amplitude.

FIG. 3 shows a diagram of brush performance over the life of atoothbrush, with the batteries being replaced periodically but stillexperiencing substantial periods of poor performance when the batteriesdischarge normally (line 30) as opposed to an appliance using the systemdescribed above (line 32), with several adjustments.

In addition to changing the drive frequency as a response to measurementof stator current and subsequent estimation of workpiece amplitudetherefrom, the battery voltage itself can be evaluated after each or aselected number of brushing events relative to a first voltagethreshold. If the measured voltage goes below the threshold, the dutycycle of the drive signal to the stator can be increased or,alternatively, the pulse width of the drive signal can be changed bypulse width modulation or similar technique. Both of these changesresult in an effective increase in the voltage supplied by the controlcircuit. As described above, this adjustment can be done more than onceduring the lifetime of the batteries, until the duty cycle or the pulsewidth has reached its maximum adjustment.

The adjustment of the duty cycle or the pulse width of the drive signalcan be used alone or combined with the change of drive frequencydescribed above in resonant drive systems to increase the efficiency ofthe system, in order to maintain performance of the battery over anextended time, even though the battery voltage may steadily decreaseduring the lifetime of the battery.

It should be understood that the change in duty cycle or pulse width ofthe drive signal and the change in drive signal frequency can beaccomplished in various ways, including by an electronic circuit or by asoftware program routine.

The above system extends the number of brushings possible fromreplaceable batteries at the desired level of performance for benefit ofthe user by improving the efficiency of the appliance, thereby reducingbattery cost to the user while maintaining desired performance of thedevice over the extended number of brushings. The number of additionalbrushings will vary, depending upon the structure of the appliance, butone example is within the range of 10-20 additional brushings.

In addition to the above, in which adjustments are made when batteryvoltage and/or workpiece amplitude goes below first thresholds, thepresent invention will terminate operation of the appliance when thebattery voltage declines below a second voltage threshold level and/orthe workpiece amplitude declines below a second amplitude thresholdlevel, at which point the battery can be replaced. For instance,relative to amplitude, if the amplitude declines below 8°, the operationof the brush will be terminated, while the drive frequency will beadjusted when the amplitude is below the first threshold but above thesecond threshold, 10° or 9° for example. The termination of operationcan also be accomplished by a circuit or by a software program routine.

Hence, the above described embodiment adjusts the duty cycle/pulse widthof the drive signal and/or adjusts the drive signal frequency tomaintain performance of the appliance over an extended time, whileterminating the operation of the brush when the voltage or amplitudedeclines below pre-established termination threshold levels, ensuringthat the brush will always be effective as long as it is operating. Asindicated above, however, the embodiment can be used with just thebattery voltage determination/evaluation or the workpiece amplitudedetermination/evaluation.

Although the above embodiment generally describes a single adjustment tothe drive signal, multiple adjustments prior to termination can be made,ultimately limited by the maximum values available in drive frequency,duty cycle and/or pulse width.

The above system can also be used for non-resonant drive systems, withjust the battery voltage determination, resulting in change in the dutycycle and/or pulse width of the drive signal, with operation of theappliance being terminated when the voltage declines below a secondselected threshold, at which point the battery can be replaced.

The compensation can also be time based, initiated by the installationof new batteries or charging of the batteries. If the appliance ischaracterized for normalized decline in performance over time,straightforward normalization compensation could be used. In such acase, when the number of uses in FIG. 2A is reached that correspondswith a pre-specified drop in performance, the duty cycle or drivefrequency could be adjusted to compensate.

Hence, in summary, battery voltage and stator current can both be used,separately or in combination, to maintain performance of resonant drivesystem appliances, while battery voltage evaluation alone can be usedfor non-resonant systems.

While the above system is useful primarily for systems using replaceablebatteries, to extend the number of brushings for a given battery, whilemaintaining consistent performance, the system can also be used forrechargeable batteries, to ensure performance of the system should thebatteries decline in charge and voltage between chargings or if thecomponents age sufficiently to affect performance. Hence, the inventionis not limited to systems using replaceable batteries, nor is it limitedto appliances using resonant drive systems, even though the system mayfind its primary use in such arrangements.

Hence, a system has been disclosed for maintaining consistentperformance of the appliance which would otherwise decline batteryvoltage during discharge of the battery and resulting decrease inbattery voltage.

Although a preferred embodiment of the invention has been disclosed forpurposes of illustration, it should be understood that various changes,modifications and substitutions may be incorporated in the embodimentwithout departing from the spirit of the invention which is defined bythe claims which follow.

What is claimed is:
 1. A system for maintaining performance of anelectric toothbrush powered by a battery, comprising: a system formeasuring the battery voltage of the electric toothbrush and/or thecurrent value in a stator portion of the motor for the electrictoothbrush from which current value the corresponding amplitude ofmovement of the workpiece of the toothbrush is then obtained; acircuit/program routine for changing the pulse width of the drive signalfor the motor if the battery voltage drops below a first voltagethreshold value and/or a circuit/program routine for changing the drivesignal frequency if the amplitude falls below a first amplitudethreshold value, to increase the amplitude of movement of the workpiece;and a circuit/program routine for terminating the operation of theappliance if the battery voltage drops below a second voltage thresholdvalue which is lower than the first voltage threshold value and/or ifthe workpiece amplitude drops below a second amplitude threshold valuewhich is lower than the first amplitude threshold value.
 2. The systemof claim 1, wherein at least one adjustment is made to the drive signalpulse width and/or the drive frequency of the toothbrush during thelifetime of the battery.
 3. The system of claim 1, wherein the batteryis a replaceable battery.
 4. The system of claim 1, wherein the batteryis rechargeable.
 5. The system of claim 1, wherein the drive frequencyis adjusted within a range up to 7 Hz.
 6. The system of claim 1, whereinthe toothbrush is driven by a resonant system.
 7. A method formaintaining performance of an electric toothbrush powered by a battery,comprising the steps of: measuring the battery voltage of the electrictoothbrush and/or the current in a stator portion of the motor for theelectric toothbrush from which the amplitude of movement of thetoothbrush is obtained; changing the pulse width of the drive signal forthe motor if the battery voltage drops below a first threshold valueand/or changing the drive signal frequency of the appliance if theamplitude falls below a first amplitude threshold value to increase theamplitude of movement of the workpiece; and terminating the operation ofthe appliance if the battery voltage drops below a second voltagethreshold value and/or if the workpiece amplitude drops below a secondamplitude threshold.
 8. The method of claim 7, wherein at least oneadjustment is made to the drive signal pulse width and/or the drivefrequency of the toothbrush during the lifetime of the battery.
 9. Themethod of claim 7, wherein the battery is a replaceable battery.
 10. Themethod of claim 7, wherein the drive frequency is adjusted within arange up to 7 Hz.
 11. The method of claim 7, wherein the electrictoothbrush is driven by a resonant system.